This invention relates to an exhaust silencer structure for outboard engines and more particularly to an outboard silencing arrangement that provides effective silencing throughout the entire engine speed range.
It has been known to provide a silencing structure for an outboard motor in which the exhaust gases are discharged through the lower unit of the engine. Specifically it has been proposed to discharge the exhaust gases through the propeller by constructing a hollow propeller through which the exhaust gases may be discharged. This system provides extremely good silencing and efficient exhaust under high speed running conditions. However, during slow running, the lower unit of the outboard is normally submerged to a greater extent than at high speed running. Thus, the exhaust output is discharged at a lower water level resulting in increased back pressure. It has, therefore, been proposed to improve exhaust efficiency during low speed running through the provision of a small exhaust outlet that is positioned above the water level and through which the exhaust gases may be discharged during low speed running. Of course, such an arrangement does not provide any significant silencing at low speed.
It is, therefore, a principal object of this invention to provide an exhaust system for an outboard engine that provides effective silencing throughout the engine speed range and also which provides for efficient exhaust gas discharge without substantial back pressure.
It is a further object of this invention to provide an improved low speed silencing system for an outboard engine.